The concurrency semaphore gates uninitialized connections across all
do_accepts loops, but was initialized to a fixed value regardless of
how many listeners exist. With multiple listeners competing for the
same units, each effectively gets less than the configured concurrency.
Initialize the semaphore to concurrency - 1 and signal 1 per listen()
call, so total capacity is concurrency - 1 + nr_listeners. This
guarantees each listener's accept loop can have at least one unit
available.
It mainly fixes problem when setting uninitialized_connections_semaphore_cpu_concurrency
config value to 1 would result in not being able to process connections, as only 1 out of 2
listeners got the semaphore.
Fixes https://scylladb.atlassian.net/browse/SCYLLADB-762
Backport: no, it's a minor problem
Closesscylladb/scylladb#28747
* github.com:scylladb/scylladb:
test: add test_uninitialized_conns_semaphore
generic_server: fix waiters count in shed log
generic_server: scale connection concurrency semaphore by listener count
9521a51e4c